ShieldWatch will add a bar to your screen displaying the total amount of damage you can absorb with spells such as Power Word: Shield, or Death Strike's Blood Shield (examples, covers any shield buff with a fixed absorb amount). It can be locked/unlocked as well as resized. It gets shields by reading your buff tooltips, very lightweight.
/shieldwatch - show help
/shieldwatch [lock/unlock] - sets bar's moving state
/shieldwatch setwidth (50-250) - set bar's width
/shieldwatch setheight (16-80) - set bar's height
Sadly I will be taking a break from WoW, so I will not be able to update my addons. I hope to be back soon, but until then, anyone who creates addons, please feel free to take over it.
1.0.3 - Sunday, May 15
Added shield timer to right side of bar, displaying the remaining time on your shortest-duration shield.
1.0.2 - Tuesday, May 10
Added a shield count to left side of bar, displaying the number of shields you have up.
1.0.1 - Thursday, May 5
Call me stupid, but I was under the impression there was a maximum of 16 buffs. ShieldWatch didn't read any buffs past the 16th. Increased this to 40.